[MUSIC PLAYING] SPEAKER: So how does someone know if they have COVID-19? Now, we're going to talk about some laboratory tests that can be used to diagnose this disease. There are two kinds of laboratory tests you might hear about for COVID-19. One is a diagnostic test, and that test identifies virus that's in the body. It's called a PCR test, which stands for polymerase chain reaction. That's the chemical reaction that's done in the lab to look for the virus. It's also called a molecular test, and it gives us a sign that the virus is reproducing in your cells. Another kind of test is an antibody test. This test can identify antibodies to the virus usually in your blood. Antibodies are made by your immune system to fight off viruses or bacteria. We can identify antibodies that are specific to this virus in your blood. Some antibodies called IgG antibodies begin to develop when you're sick, but they're identified mostly after you recover. Remember that no tests are perfect. This means that sometimes, despite our best efforts, the results from the test could be wrong. When we're looking for active infection, usually, we do PCR tests on people who have current signs and symptoms of the disease. The PCR test detects the RNA of the virus, which means the genetic material of the virus. So this tells us, essentially, if the virus is in the body and replicating in the body. We usually take a swab from the nose, the throat, or the mouth somewhere in our respiratory tract. Saliva can also be tested for the virus, but it's not commonly used. The reason we take samples from the respiratory tract is because that's where the virus likes to replicate in the body. If someone has a positive PCR test, that shows that there are particles of that virus in the sample that was taken. This means there is an active infection there. Sometimes, there are false results, and that means that someone actually is infected with the virus, but their sample doesn't show that the virus is there. So not all people with the infection will have the viral RNA in their sample. This is important to keep in mind that just because someone has a negative PCR test that doesn't necessarily mean that they definitely don't have the infection. However, if someone does have a positive PCR test, then we can be very confident that they do have COVID-19. Sometimes, we want to know if someone has had the infection in the past. An IgG antibody test is the most common antibody test used for this purpose. Our bodies usually start to produce IgG antibodies 10 to 14 days after we're infected. So they'll start to develop when we're sick, but we'll be better able to identify them after we've recovered. So these antibody tests can be performed after someone has already recovered from the infection or in people who've never had signs and symptoms but want to know if they have been infected. Remember that some people are infected but never have signs and symptoms. A positive IgG antibody test means that you were infected with the virus in the past, but it doesn't tell us when you were infected. So if you have IgG antibodies in your blood, that could mean that you have some protection from future SARS coronavirus to infections. However, we don't know how long that protection will last, and we don't really know how good that protection is yet. So this is something that we're actively trying to learn more about. So to summarize again, there are two types of tests, a diagnostic test and a test to see if you had a past infection. The diagnostic test takes a sample from your respiratory tract. This figure shows a swab being collected from the back of the throat going in through the nose. That will tell us whether or not there's viral RNA detectable in your respiratory tract, suggesting that you have an active infection. By the time you recover, you'll develop IgG antibodies, and if we take a sample of your blood, we can detect those and we can determine if you were infected in the past. Neither of these tests are perfect, but they're very useful tools for identifying people who have had disease and who are currently infected. [MUSIC PLAYING]